It doesn't look like a loop, but probably some trunk in the network is bouncing pretty regularly. Each time it goes up or down, STP holds a new root bridge election and/or new paths to the root bridge. As this occurs, various ports will be changed between forwarding and blocking, and hosts may appear to be coming from different directions (ports) after each transition.
You need to go through the trunks in the network to find which one is bouncing.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...